The invention relates generally to thermal barrier coating systems, in particular, thermal barrier coating systems exposed to high temperatures such as in a gas turbine engine.
Higher operating temperatures for gas turbine engines have been continuously sought in the art in order to improve the operating efficiency of the engine. However, as operating temperatures are raised, the high temperature capabilities of the components in the engine must also increase. To this end, various nickel-base and cobalt-base superalloys have been employed, which incorporate oxidation-resistant and corrosion-resistant overlay and diffusion-type coatings.
Further improvements in the high temperature capabilities of components have been realized by coating engine components with a thermal barrier coating (TBC), in addition to the overlay and diffusion-type coatings mentioned above. TBCs are generally formed of ceramic materials, such as zirconia (ZrO2) stabilized by an oxide material. To promote adhesion between the thermal barrier coating and the underlying substrate, bond coats are utilized. One type of bond coat is formed of MCrAlY, wherein M is chosen from the group consisting of iron, cobalt, nickel and combinations thereof.
Such bond coats may be deposited thermal spray techniques, including low pressure plasma spray (LPPS), High Velocity-Oxy Fuel (HVOF), and air plasma spray (APS). Of these bond coats, APS bond coats have been used for their ease of deposition and bond quality and integrity between the substrate and the TBC. However, a need exists in the art for further improved bondcoats of a thermal barrier coating system. Such bondcoats should be easily deposited, have improved oxidation-and/or corrosion-resistance, and provide a good adhesive interface for the overlying thermal barrier coating.
In one embodiment of the present invention, a method for forming a thermal barrier coating system on a turbine engine component is provided. The method includes forming a bondcoat on the turbine engine component by thermally co-spraying first and second distinct alloy powders on the turbine engine component, to form an oxidation-resistant region. Then, a bonding region is provided by thermally spraying a third alloy powder on the oxidation-resistant region. The oxidation-resistant region is more resistant to oxidation than the bonding region. A thermal barrier coating is then deposited so as to overlie the bondcoat.
In another embodiment of the present invention, a turbine engine component is provided. The component includes a substrate, and a bondcoat overlying the substrate. The bondcoat has an oxidation-resistant region, and a bonding region overlying the oxidation-resistant region, wherein the oxidation-resistant region is more resistant to oxidation than the bonding region. A thermal barrier coating overlies the bondcoat.